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High-performance and stability for protonic ceramic fuel cell cathode applications are realised in a self-assembled nanocomposite material Ba0.5Sr0.5(Co0.7Fe0.3)0.6875W0.3125O3−δ (BSCFW) through interplay of single and double perovskite phases.

Li-rich rocksalt oxides are promising candidates as high-energy density cathode materials for next-generation Li-ion batteries because they present extremely diverse structures and compositions. Most reported materials in this family contain as many cations as anions, a characteristic of the ideal cubic closed-packed rocksalt composition. In this work, a new rocksalt-derived structure type is stabilized by selecting divalent Cu and pentavalent Sb cations to favor the formation of oxygen vacancies during synthesis. The structure and composition of the oxygen-deficient Li4CuSbO5.5□0.5 phase is characterized by combining X-ray and neutron diffraction, ICP-OES, XAS, and magnetometry measurements. The ordering of cations and oxygen vacancies is discussed in comparison with the related Li2CuO2□1 and Li5SbO5□1 phases. The electrochemical properties of this material are presented, with only 0.55 Li+ extracted upon oxidation, corresponding to a limited utilization of cationic and/or anionic redox, whereas more than 2 Li+ ions can be reversibly inserted upon reduction to 1 V vs Li+/Li, a large capacity attributed to a conversion reaction and the reduction of Cu2+ to Cu0. Control of the formation of oxygen vacancies in Li-rich rocksalt oxides by selecting appropriate cations and synthesis conditions affords a new route for tuning the electrochemical properties of cathode materials for Li-ion batteries. Furthermore, the development of material models of the required level of detail to predict phase diagrams and electrochemical properties, including oxygen release in Li-rich rocksalt oxides, still relies on the accurate prediction of crystal structures. Experimental identification of new accessible structure types stabilized by oxygen vacancies represents a valuable step forward in the development of predictive models., Controlling the composition and synthesis conditions of Li-rich rocksalt oxides can lead to to new structure types stabilized by oxygen vacancies. The complex atomic ordering of Li4CuSbO5.5 is described and discussed in the context of other oxygen-deficient rocksalt oxides.

The synthesis of three-dimensional (3D) covalent organic frameworks (COFs) requires high-connectivity polyhedral building blocks or the controlled alignment of building blocks. Here, we use the latter strategy to assemble square-planar cobalt(II) phthalocyanine (PcCo) units into the nbo topology by using tetrahedral spiroborate (SPB) linkages that were chosen to provide the necessary 90° dihedral angles between neighboring PcCo units. This yields a porous 3D COF, SPB-COF-DBA, with a noninterpenetrated nbo topology. SPB-COF-DBA shows high crystallinity and long-range order, with 11 resolved diffraction peaks in the experimental powder X-ray diffraction (PXRD) pattern. This well-ordered crystal lattice can also be imaged by using high-resolution transmission electron microscopy (HR-TEM). SPB-COF-DBA has cubic pores and exhibits permanent porosity with a Brunauer-Emmett-Teller (BET) surface area of 1726 m2 g-1.

The piezoelectric devices widespread in society use noncentrosymmetric Pb-based oxides because of their outstanding functional properties. The highest figures of merit reported are for perovskites based on the parent Pb(Mg1/3Nb2/3)O3 (PMN), which is a relaxor: a centrosymmetric material with local symmetry breaking that enables functional properties, which resemble those of a noncentrosymmetric material. We present the Pb-free relaxor (K1/2Bi1/2)(Mg1/3Nb2/3)O3 (KBMN), where the thermal and (di)electric behavior emerges from the discrete structural roles of the s0 K+ and s2 Bi3+ cations occupying the same A site in the perovskite structure, as revealed by diffraction methods. This opens a distinctive route to Pb-free piezoelectrics based on relaxor parents, which we demonstrate in a solid solution of KBMN with the Pb-free ferroelectric (K1/2Bi1/2)TiO3, where the structure and function evolve together, revealing a morphotropic phase boundary, as seen in PMN-derived systems. The detailed multiple-length-scale understanding of the functional behavior of KBMN suggests that precise chemical manipulation of the more diverse local displacements in the Pb-free relaxor will enhance performance.

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σo ) and electronic conductivity (σe ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σe but inadequate σo . It has been a long-standing challenge to develop MIECs with both high σo and stability under device operation conditions. For example, the well-known perovskite oxide Ba0.5 Sr0.5 Co0.8 Fe0.2 O3- δ (BSCF) exhibits exceptional σo and electrocatalytic activity. The reactivity of BSCF with CO2 , however, limits its use in practical applications. Here, the perovskite oxide Bi0.15 Sr0.85 Co0.8 Fe0.2 O3- δ (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σo among the highest for known MIECs, but also high CO2 tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO2 . The combination of high oxide transport properties and CO2 tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.

Highly dense CaMn1-xRexO3 (0 ≤ x ≤ 0.04) samples were prepared by solid-state synthesis. The effect of Re doping was assessed by the characterisation of crystal structure, oxygen content, and electrical and thermal transport properties. The oxidation state of the substituted Re was determined by X-ray absorption near edge spectra to be Re7+, and led to expansion of the lattice and an increase in electron carrier concentration due to the formation of Mn3+. The thermal behaviour of the electrical conductivity and the thermopower over a wide temperature range allowed identification of different conduction mechanisms: (1) below 110 K, 3D variable range hopping, (2) between 110 and 650 K, small polaron transport, and (3) above 650 K, activation of carriers over a mobility edge. Evaluation of the power factor expected for different dopant oxidation states as a function of dopant concentration shows that the doping strategy using a heavy heptavalent ion allows accessibility of the peak power factor at lower dopant concentrations, lowering the amount of non-ionised impurities, and therefore improves the electronic substitution efficiency, the ratio of activated carriers over the nominal doping concentration, compared to previously studied dopants. An increased power factor and a reduced lattice thermal conductivity are obtained with a peak figure of merit ZT = 0.16(3) at 947 K for CaMn0.98Re0.02O3. This is an approximately two-fold increase compared to undoped CaMnO3, and is comparable to the highest values reported for highly dense B-site doped CaMnO3.

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σ

It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1–xLixO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1–xLixO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient ...

Tilting toward two properties Opposing electronic and symmetry constraints can make it difficult to combine some pairs of material properties in a single crystalline material. Magnetization and electrical polarization are such a pair, but their combination could be useful for applications such as magnetoelectric information storage. Pitcher et al. now show that careful design of chemical substitutions in a layered perovskite are both electrically polar and weakly ferromagnetic at temperatures up to 330 K. Science , this issue p. 420

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO3-type cation ordering that breaks inversion symmetry may be combined with long-range magnetic ordering of high spin d5 cations above room temperature in the AFeO3 system. We report the synthesis of a polar corundum GaFeO3 by a high-pressure, high-temperature route and demonstrate that its polarity arises from partial LiNbO3-type cation ordering by complementary use of neutron, X-ray, and electron diffraction methods. In situ neutron diffraction shows that the polar corundum forms directly from AlFeO3-type GaFeO3 under the synthesis conditions. The A3+/Fe3+ cations are shown to be more ordered in polar corundum GaFeO3 than in isostructural ScFeO3. This is explained by DFT calculations which indicate that the extent of ordering is dependent on the configurational entropy available to each system at the very different synthesis temperatures required to form their corundum structures. Polar corundum GaFeO3 exhibits weak ferromagnetism at room temperature that arises from its Fe2O3-like magnetic ordering, which persists to a temperature of 408 K. We demonstrate that the polarity and magnetization are coupled in this system with a measured linear magnetoelectric coupling coefficient of 0.057 ps/m. Such coupling is a prerequisite for potential applications of polar corundum materials in multiferroic/magnetoelectric devices.

The polar corundum structure type offers a route to new room temperature multiferroic materials, as the partial LiNbO

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3.

The (AO)(ABO3)n Ruddlesden-Popper structure is an archetypal complex oxide consisting of two distinct structural units, an (AO) rock salt layer separating an n-octahedra thick perovskite block. Conventional high-temperature oxide synthesis methods cannot access members with n > 3, but low-temperature layer-by-layer thin film methods allow the preparation of materials with thicker perovskite blocks, exploiting high surface mobility and lattice matching with the substrate. This paper describes the growth of an n = 6 member CaO[(CSMO)2(LCMO)2 (CSMO)2] in which the six unit cell perovskite block is sub-divided into two central La0.67Ca0.33MnO3 (LCMO) and two terminal Ca0.85Sm0.15MnO3 (CSMO) layers to allow stabilization of the rock salt layer and variation of the transition metal charge.

Solid oxide fuel cells (SOFCs) are a major candidate technology for clean energy conversion because of their high efficiency and fuel flexibility.1 The development of intermediate-temperature (500–750 °C) SOFCs requires electrolytes with high oxide ion conductivity (exceeding 10−2 S cm−1 assuming an electrolyte thickness of 15 μm1). This conductivity, in turn, necessitates enhanced understanding of the mechanisms of oxide ion charge carrier creation and mobility at an atomic level. The charge carriers are most commonly oxygen vacancies in fluorites2, 3 and perovskites.3, 4 There are fewer examples of interstitial-oxygen-based conductors such as the apatites5, 6 and La2Mo2O9-based materials,7–9 so information on how these excess anion defects are accommodated and the factors controlling their mobility is important.

This paper reports the evaluation of the cubic B site cation-ordered double perovskite system Ba2Co2−x(Mo1/2Nb1/2)xO6, resulting in the single phase composition Ba2CoMo0.5Nb0.5O6−δ (BCMN) with a mixed Co charge state stabilized by a combination of Mo and Nb doping as a new mixed conductor with potential SOFC cathode applications. X-ray, neutron, and electron diffraction show that hexagonal intergrowths found in multiple phase samples at lower Mo/Nb contents are suppressed in BCMN, which has large domains of rock-salt ordered B site cations with separate Co and Mo/Nb sites. Conductivity measurement and impedance spectroscopy investigation shows that BCMN has a considerably reduced dc conductivity compared with materials such as BSCF but exhibits comparable electrochemical properties to some existing cathode materials in symmetrical cell measurements, and shows higher structural stability and reduced reactivity with the Ce0.8Sm0.2O2−δ (SDC) electrolyte. The role of Mo in dioxygen activation is proposed to o...

The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 A(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.

Microporous poly(tri(4-ethynylphenyl)amine) networks were synthesized by palladium-catalyzed Sonogashira−Hagihara cross-coupling chemistry with apparent Brunauer−Emmet−Teller (BET) specific surface areas in the range 500−1100 m2/g. It was found that very fine synthetic control over physical properties such as BET surface area, Langmuir surface area, micropore surface area, micropore volume, and bulk density could be achieved by varying the average monomer strut length. The micropore structure and micropore surface area were rationalized by atomistic simulations for one network, NCMP-0, based on multiple physical characterization data.

A2B2O7 complex oxides with the pyrochlore structure feature a wide variety of chemical compositions and corresponding diverse electrical and physical properties. A new pyrochlore, Yb0.96Ca1.04TiNbO6.98, is reported and characterized in terms of structural stability and electrical properties. The material is stable to ∼1450 °C in 5% H2/N2 and has a high electronic conductivity in a reducing atmosphere, e.g., 9 S/cm at 800 °C in 5% H2/N2 after high-temperature reduction. Other cation substitutions enhance the low-temperature kinetics of conductivity response to changes in oxygen partial pressure.

A series of rigid microporous poly(aryleneethynylene) (PAE) networks was synthesized by Sonogashira-Hagihara coupling chemistry. PAEs with apparent Brunauer-Emmet-Teller surface areas of more than 1000 m(2)/g were produced. The materials were found to have very good chemical and thermal stability and retention of microporosity under a variety of conditions. It was shown that physical properties such as micropore size, surface area, and hydrogen uptake could be controlled in a "quantized" fashion by varying the monomer strut length, as for metal-organic and covalent organic frameworks, even though the networks were amorphous in nature. For the first time, it was demonstrated that these properties can also be fine-tuned in a continuous manner via statistical copolymerization of monomer struts with differing lengths. This provides an unprecedented degree of direct synthetic control over micropore properties in an organic network.

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La1.54Sr0.46Ga3O7.27 stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02–0.1 S cm−1 over the 600–900 ∘C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions. Fast-ion conductors are needed to reduce the operating temperature of solid-oxide fuel cells. The identification of the conduction mechanism in electrolytes where conduction is based on mobile oxygen interstitials rather than the usual anion vacancies offers a generic design principle for novel solid electrolytes.

Well-characterized bulk materials in the candidate dilute magnetic semiconductor system In 2-x Cr x O 3 are prepared for 0

A 21R-type mixed conducting oxygen-deficient hexagonal perovskite Ba7Y2Mn3Ti2O20 was synthesized and its structure characterized by variable temperature neutron powder diffraction. The structure is characterized by the presence of both BaO2 and BaO3 layers. In the oxygen-stoichiometric material, the vacancies are ordered in c‘-BaO2 layers. Extra oxygen is accommodated by intergrowth of the vacancy-ordered c‘-BaO2 layers with cubic c-BaO3-x layers (x ≅ 1), which have disordered 2/3 oxygen occupancy. This material displays mixed electronic and oxide ionic conduction at high temperature, and the role of the two distinct and partially occupied anion sites within the BaO2 layers in permitting the oxygen mobility is discussed.

A series of hypercrosslinked polymer networks has been synthesized by the self-condensation of bischloromethyl monomers such as dichloroxylene (DCX), 4,4‘-bis(chloromethyl)-1,1‘-biphenyl (BCMBP), and 9,10-bis(chloromethyl)anthracene (BCMA). These materials are predominantly microporous and exhibit Brunauer−Emmett−Teller (BET) surface areas of up to 1904 m2/g as measured by N2 adsorption at 77.3 K (Langmuir surface area = 2992 m2/g). Networks based on BCMBP exhibit a gravimetric storage capacity of 3.68 wt % at 15 bar and 77.3 K, the highest yet reported for an organic polymer. The micro- and mesostructure of the networks is explained by a combination of solid-state NMR, gas sorption measurements, pycnometry, and molecular simulations. The isosteric heat of sorption for H2 on these materials is found to be in the range 6−7.5 kJ/mol. A molecular model is presented for a p-DCX network that simulates well certain key physical properties such as pore volume, pore width, absolute density, and bulk density. This...

Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory1, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required2. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials3. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field4,5. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons6. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics7,8. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure9 precludes bulk magnetization and linear magnetoelectric coupling10. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization11 with glassy magnetization, although it lacks long-range magnetic order12. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets13, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary14 (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3–PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.

Chevrel phase superconductors have high upper critical fields, which make them candidate materials for the next generation of high field magnets operating at fields significantly above 25 T. The effect of doping lead-molybdenum-sulphide with europium ((Pb/sub 1-x/Eu/sub x/)Mo/sub 6/S/sub 8/ with x=0.0, 0.25, 0.5, 0.75 and 1.0) has been investigated. Bulk materials were fabricated using different heat-treatment procedures, followed by hot isostatic pressing at a pressure of 2000 Bar and a temperature of 800/spl deg/C, X-ray diffraction data have been taken. Resistivity and susceptibility measurements have been made in magnetic fields up to 15 T, and temperatures from 3.5 K to 18 K. Single-phase samples were fabricated with x=0.0, 0.25 and 0.5. The x=0.0 sample has an onset critical temperature of 15.16 K. For x=0.25, the critical temperature decreased to 12.62 K but the upper critical field calculated for zero temperature increased from 51 T to 57 T.

Bulk polycrystalline materials of the quaternary superconducting Chevrel phase (Pb/sub 1-x/Cu/sub 1.8x/)Mo/sub 6/S/sub 8/ with x=0.00, 0.05, 0.10, 0.30, 0.50 and 1.00 have been fabricated using HIP'ing at a pressure of 2000 bar and a temperature of 800/spl deg/C for 8 hr. The phase structure and hexagonal lattice parameters (c, a) have been studied using X-ray diffraction. Resistivity and susceptibility measurements have been made in magnetic fields up to 15 T and temperatures from 3.5 K to 18 K. The ternary Chevrel phase compounds PbMo/sub 6/S/sub 8/ and Cu/sub 1.8/Mo/sub 6/S/sub 8/ have been fabricated with high c/a ratio and critical temperature (resistive midpoints of 14.8 K and 11.1 K respectively). When x/spl les/0.1, quaternary materials are almost single phase. When x>0.1, the quaternary material are a two-component mixture of PbMo/sub 6/S/sub 8/-like and Cu/sub 1.8/Mo/sub 6/S/sub 8/-like structures. The materials have broad transitions with calculated upper critical field values for 0 K of /spl sim/40 T determined from the midpoint of the resistive transition.

High surface area porous poly(phenylene butadiynylene) networks were obtained (BET surface area up to 842 m(2) g(-1)) by the palladium-catalyzed homocoupling of 1,3,5-triethynylbenzene and 1,4-diethynylbenzene.

Bi2ZnTiO6, a lead-free analogue of PbTiO3, has been prepared by high-pressure solid-state synthesis methods. Structural analysis reveals that the tetragonal distortion (c/a ratio = 1.21) of Bi2ZnTiO6 is the largest reported for any d0 B site Pb or Bi based perovskite. Significant cation displacements result in a point-charge calculated polarization of 150 μC cm-2.

Chevrel phase PbMo 6 S 8 (PMS) superconducting powder ball-milled from 5 to 200 h has been investigated using X-ray diffraction (XRD) and scanning and transmission electron microscopy. Ball milling produced particles with crystallites of PMS in the range 10–100 nm and amorphous phase. From XRD data, it was found that the crystallite size decreased and lattice strain increased with increasing milling time until by 200 h the material was predominantly amorphous. The powder ball-milled for 100 h was subsequently annealed at temperatures from 400 to 1000 °C for 8 h. Annealing at 600 °C and above released the lattice strain. At 800 °C and above the amorphous phase crystallised and grains coarsened with sizes in the range 50–100 nm.

The large band gap (3.58 eV) and dielectric properties (e r =50) of bulk SrHf0.67Ti0.33O3 (SHTO) make it a promising high-k material. SHTO films were deposited on p-type (100) Si single crystal substrates by pulsed laser deposition. The composition, structure, thickness, and roughness of the SHTO films have been studied using X-ray Photoelectron Spectroscopy, X-ray reflectivity, transmission electron microscopy, and atomic force microscopy. The capacitance–voltage and leakage current density characteristics of the films have been evaluated. For a post-annealed SHTO film with a thickness of 25 nm, the relatively high permittivity of 35 was achieved with the low leakage current density of 4.96×10−4 A/cm2 at −2 V bias voltage.

NdBaCo2O5+δ films have been grown on (001)-SrTiO3 substrates using pulsed laser deposition with RHEED to access both A-site ordered and A-site disordered films grown in a layer-by-layer manner. Ionic diffusion kinetics are shown to be key parameter for A-site order, attained by control of growth kinetics, mobility, and supersaturation.

This paper reports the evaluation of the cubic B site cation-ordered double perovskite system Ba2Co2−x(Mo1/2Nb1/2)xO6, resulting in the single phase composition Ba2CoMo0.5Nb0.5O6−δ (BCMN) with a mixed Co charge state stabilized by a combination of Mo and Nb doping as a new mixed conductor with potential SOFC cathode applications. X-ray, neutron, and electron diffraction show that hexagonal intergrowths found in multiple phase samples at lower Mo/Nb contents are suppressed in BCMN, which has large domains of rock-salt ordered B site cations with separate Co and Mo/Nb sites. Conductivity measurement and impedance spectroscopy investigation shows that BCMN has a considerably reduced dc conductivity compared with materials such as BSCF but exhibits comparable electrochemical properties to some existing cathode materials in symmetrical cell measurements, and shows higher structural stability and reduced reactivity with the Ce0.8Sm0.2O2−δ (SDC) electrolyte. The role of Mo in dioxygen activation is proposed to o...

The two-dimensional polyhedral anion network melilites La1+xSr1−xGa3O7+0.5x exhibit interstitial oxide ion conductivity. The solid solution is shown to extend to x = 0.64, and the variation of the conductivity with x is investigated. At high temperatures, all of these compounds adopt the typical tetragonal melilite structure. When x > 0.6, cooling below 600 °C results in a reversible phase transition to an orthorhombic structure which reduces the ionic conductivity. Quenching experiments have shown the tetragonal structure has a higher conductivity compared to the orthorhombic structure of the same composition. Short-range order effects associated with this transition exercise an important influence on the composition- and temperature-dependence of the conductivity.

The assembly of multifunctional nanocomposite materials is demonstrated by exploiting the molecular sieving property of SBA-16 nanoporous silica and using it as a template material. The cages of the pore networks are used to host iron oxide magnetic nanoparticles, leaving a pore volume of 0.29 cm3 g-1 accessible for drug storage. This iron oxide-silica nanocomposite is then functionalized with amine groups. Finally the outside of the particle is decorated with antibodies. Since the size of many protein molecules, including that of antibodies, is too large to enter the pore system of SBA-16, the amine groups inside the pores are preserved for drug binding. This is proven using a fluorescent protein, fluorescein-isothiocyanate-labeled bovine serum albumin (FITC-BSA), with the unreacted amine groups inside the pores dyed with rhodamine B isothiocyanate (RITC). The resulting nanocomposite material offers a dual-targeting drug delivery mechanism, i.e., magnetic and antibody-targeting, while the functionalization approach is extendable to other applications, e.g., fluorescence-magnetic dual-imaging diagnosis.

High permittivity SrHf0.5Ti0.5O3 films (k=62.8) have been deposited on (001) Nb–SrTiO3 single crystal conducting substrates by pulsed laser deposition. The SrHf0.5Ti0.5O3 films grow epitaxially with atomically smooth surfaces (root mean square roughness 4.8 A) and a c-axis orientation parallel to the substrate. The measured band gap of SrHf0.5Ti0.5O3 is 3.47 eV compared with 3.15 eV in SrTiO3. Under an applied electric field of 600 kV/cm, the leakage current density of the SrHf0.5Ti0.5O3 films is 4.63×10−4 A/cm2. These attractive dielectric properties and enhanced band gap values make SrHf0.5Ti0.5O3 a promising candidate for high-k dielectric applications in silicon-based integrated circuits.

A2B2O7 complex oxides with the pyrochlore structure feature a wide variety of chemical compositions and corresponding diverse electrical and physical properties. A new pyrochlore, Yb0.96Ca1.04TiNbO6.98, is reported and characterized in terms of structural stability and electrical properties. The material is stable to ∼1450 °C in 5% H2/N2 and has a high electronic conductivity in a reducing atmosphere, e.g., 9 S/cm at 800 °C in 5% H2/N2 after high-temperature reduction. Other cation substitutions enhance the low-temperature kinetics of conductivity response to changes in oxygen partial pressure.